The present invention generally relates to a vacuum contactor. Preferably, it relates to one including a contactor housing, a drive coil, an armature, an operating element and at least one vacuum contact. Even more preferably, the drive coil deflects the armature from an armature rest position to an armature operating position when a pull-in current is applied. The deflection of the armature then causes the operating element to be deflected from an element rest position to an element operating position. Finally, the deflection of the operating element results in closing of the at least one vacuum contact.
CH-A-169 467 discloses a vacuum contactor having a contactor housing, a drive coil, an armature, an operating element and at least one vacuum contact:
with the drive coil deflecting the armature from an armature rest position to an armature operating position when a pull-in current is applied,
with the deflection of the armature causing the operating element to be deflected from an element rest position to an element operating position,
with the deflection of the operating element resulting in opening of the at least one vacuum contact,
with, when the armature is deflected from the armature rest position to the armature operating position, the armature first of all passing through an initial movement distance, and then passing through a driving movement distance, and
with the operating element being deflected by the armature only while the latter is passing through the driving movement distance
GB 1 432 372 A discloses an air contactor having a contactor housing a drive coil, an armature, an operating element and at least one contact
with the drive coil deflecting the armature from an armature rest position to an armature operating position when a pull-in current is applied.
with the deflection of the armature causing the operating element to be deflected from an element rest position to an element operating position.
with the deflection of the operating element resulting in closing of the at least one contact,
with, when the armature is deflected from the armature rest position to the armature operating position, the armature first of all passing through an initial movement distance, followed by a driving movement distance, and
with the operating element being deflected by the armature only while the latter is passing through the driving movement distance.
In contactors, the armature and the operating element, together with the armature, are generally deflected against a spring force when the pull-in current is applied to the drive coil. The spring force thus acts in the direction of the armature rest position and of the element rest position. This spring force must be overcome by the pull-in force which the drive coil exerts on the armature as a result of the pull-in current. The pull-in force is dependent on the pull-in current, which is in turn dependent on the supply voltage that is supplied to the drive coil.
Both the pull-in force and the spring force in the opposite direction vary along the distance through which the armature and the operating element are deflected. If the contactor is not well designed, it is thus possible for a situation to occur in which, if the supply voltage is too low, although the armature and the operating element are deflected from their rest positions, the armature and the operating element are not deflected to their operating positions, however. In a case such as this, the armature and operating element either remain stuck in an intermediate position, or a contact which is operated by the operating element is only operated without a pressure. Depending on the duration of this state, this can lead to high wear, and generally also to damage, while in the extreme case, it can even lead to destruction of the contactor.
In the case of air contactors, that is to say in contactors whose contacts are surrounded by air, it is possible to design these contactors such that the armature and operating element are either not deflected at all from their rest positions or else are moved completely to their operating positions. Such a contactor characteristic is referred to as a tripping characteristic.
Vacuum contactors require a greater spring force in the opposite direction than air contactors. This is because the vacuum pressure forces which would initiate autonomous operation of the contacts must be overcome. Until now, for vacuum contactors, it has been regarded as being impossible to achieve a tripping characteristic just on the basis of the mechanical/electrical design of the contactor. Vacuum contactors according to the prior art therefore either do not have a tripping characteristic or else drive electronics are connected upstream of the drive coil and apply the supply voltage to the drive coil only when the supply voltage is high enough to ensure that the armature and operating element will reliably be moved to the operating positions.
In an embodiment of the present invention, if the vacuum contactor is designed in a suitable manner, it is possible to achieve a tripping characteristic even without any upstream drive electronics. A vacuum contactor has been created, in one embodiment of the present application, in which the operating element always either remains in the element rest position or is deflected completely to the element operating position when a current that is less than the pull-in current is applied to the drive coil.
This can occur because, for example, the force which needs to be overcome along the initial movement distance can be chosen independently of the contact arrangement. In particular, it can be chosen independently of the fact that vacuum contacts are being operated. This allows a tripping characteristic to be achieved, if the vacuum contactor is designed in a suitable manner.
In vacuum contactors, arcs can be quenched even with small contact openings. Vacuum contactors therefore generally have shorter switching movements than air contactors. The dimensions that are known for air contactors can thus be used, provided the sum of the initial movement distance and the driving movement distance correspond to the contact movement distance of an air contactor. In practice, this corresponds to the ratio of the initial movement distance to the driving movement distance being between 1:3 and 3:1. In general, the ratio of the initial movement distance to the driving movement distance is between 2:3 and 3:2.
As already mentioned, the armature can be deflected against an initial movement force while it is passing through the initial movement distance, and against a driving force while it is passing through the driving movement distance. A tripping characteristic can be achieved in a particularly highly reliable manner if the initial movement force is less than the driving force. In practice, this normally means that the ratio of the initial movement force to the driving force is between 1:10 and 1:2, in particular between 1:5 and 1:4.
The physical design of the vacuum contactor can be particularly simple if the initial movement force is applied by an initial movement spring device, and the driving force is applied by a driving spring device, the initial movement spring device is supported firstly on the armature and secondly on the operating element, and the driving spring device is supported firstly on the operating element and secondly on the contactor housing.
If the operating element has a stop, against which the armature is moved when it is deflected from the armature rest position, the initial movement distance can be defined exactly in a particularly simple manner.